Water Retention of Two Types of Hexane-Defatted Corn Germ Proteins and Soy Protein Flour'

Cereal Chem. 66(l):51 -55 Water retention properties of two hexane-defatted corn germ protein retention of both CGP preparations. Time of incubation (10-30 min) and (CGP) preparations processed by a modified and a conventional procedure pH of solution (pH 6-7) did not affect water retention. Defatted CG P and soy protein flour were studied in model systems and analyzed using obtained by the modified process had higher water retention (2.04) at low response surface methodology. The protein preparations had different fat incubation temperatures than that processed by conventional procedure and protein contents. The defatted CGP obtained by the modified process (1.49). Time and temperature of incubation and pH had no significant was whiter, less red, and less yellow than defatted CGP processed effect on the water retention of soy protein flour. Soy flour had higher conventionally and was similar in color to soy protein flour. Increased water retention than defatted CGP at temperatures lower than 550 C due to temperature of incubation in the range 5-80C enhanced the water its higher protein content. Water retention is a basic functional property of food components such as proteins and carbohydrates. Water retention of plant proteins has been studied by Karmas (1973), Fleming et al (1974), Lucisano et al (1984), Luallen (1985), Jones and Tung (1983), Lin and Zayas (1987) and others. Even though it may have all prerequisites to be nutritionally superior, a protein will have no effect on human nutrition unless it can be successfully incorporated into food systems (Ryan 1977). Food ingredients of plant origin with a high content of carbohydrates were reported to neither participate in the waterbinding property nor improve the emulsifying capacity of meat emulsions (Mittal and Usborne 1985). However, it was found that carbohydrate-rich corn protein had high water retention (Lucisano et al 1984, Bhattacharya and Hanna 1985, Luallen 1985). The 'Contribution no. 88-423-J from the Kansas Agricultural Experiment Station, Manhattan. 2Department of Foods and Nutrition, Kansas State University, Manhattan 66506. 'Present address: Department of Food Science, National Ping Tung Institute of Agriculture, Ping-Tung, Taiwan, Republic of China. © 1989 American Association of Cereal Chemists, Inc. functional properties of protein ingredients from cereal sources, such as water retention and fat binding, justify the use of these relatively low-cost raw materials. Soy products provide a variety of protein ingredients: flour, concentrate, isolate, and their modified products. However, the uses of soybean proteins have been limited because of the strong beany, grassy, and bitter flavors associated with these proteins (Kinsella 1979). Defatted corn germ protein (DCGP) has considerable potential for use as a supplement in a variety of foods as a new protein source. A good corn germ protein source can be obtained by drying corn germ meal at low temperatures and extracting the oil by solvent extraction (Lucisano et al 1984). At present, the conventional oil-extraction process with hexane as a solvent leaves residual lipids in the flour that reduce its quality (Phillips and Sternberg 1979). Oxidation of this residual oil in DCGP produces an unpleasant off flavor in the product, and sufficient storage stability cannot be obtained because of incomplete fat extraction. In the production of DCGP, particularly during fat extraction, removal of hexane residues using the conventional desolventization procedure can damage the finished product due to changes in Vol. 66, No. 1, 1989 51 flavor and color resulting from protein denaturation and a browning reaction. Recently, Christianson et al (1984) studied a supercritical CO2 method for extracting oil from corn germ meal and obtained a food-grade quality DCGP safe and palatable for human consumption. However, currently the corn milling industry is using a hexane-extraction process. Functional properties of DCGP preparations reflect the composition of the sample; the nature and reactivity of the proteins; their native structure; and interactions with nonprotein components of DCGP preparations, carbohydrates, and lipids. They are affected also by environmental and processing conditions such as temperature of incubation and pH. There is a little information related to water retention of DCGP (Lin and Zayas 1987). Although the individual functional properties of several kinds of corn proteins and DCGP have been studied (Peri et al 1983, Lucisano et al 1984, Lin and Zayas 1987), little work has been done to evaluate water retention properties of hexane-defatted CGP. The objective of this study was to investigate the water retention of two hexane-defatted CGPs and soy protein preparations in order to obtain information related to their water retention capacity in the range of pH and temperature experienced during sausage manufacturing. Two DCGP obtained by conventional and modified fat-extraction methods were tested. MATERIALS AND METHODS Two hexane-defatted CGP preparations were used in the experiments. DCGP was obtained after hexane fat extraction in dry milling operations. One hexane-defatted CGP was processed by the conventional method and the other by the modified technique. Soy flour (Soya fluff 200W) used as a control was obtained from the Central Soya, Inc. (Chemurgy Division, Fort Wayne, IN).